Electrolytic etching machine



' 2 Sheets-Shae? 1 E. G. HARTEL ELECTROLYTIC mcnme momma Filed Nov. 20, 1935 2 mecuowno u M 1 .I. I 2 0 A U I ..W.uIw 11 v 4 H Jan. 3, 1939.

Jan. 3, 1939. E, GHAMEL 2,142,512

ELECTROLYTIC ETCHING MACHINE Filed Nqv. 20, 1935 2 Sheets-Sheet 2 Fig. 5'.

197' ERA/m Patented Jan. 3, 1939 PATENT OFFICE snsc'motmc a'rcnmo mom Ernest Gordon Bartel, Middlesex, England Application November 20, 1935, Serial No. 50,721 In Great Britain November 24, 1934 12 Claims.

This invention relates to etching by electrolytic methods. It is concerned particularly with the etching of zinc plates but is also applicable to other metals. It will be mainly described as applied to flat plates but it will be recognized that it is applicable also to articles which are of approximately flat or regularly curved forms. The word "plate used in this specification is to be understood to extend to such forms unless the context indicates otherwise.

In an electrolytic etching machine, the plate.

to be etched for'msthe anode and the current flow carries metal from it into and through the electrolyte towards the cathode. It has been found that, in many cases, a uniformrate of etching over the whole face of a plate is not obtained, the removal of metal being more rapid near the sides than near the centre. cases, the etching action extends round the edges to the back of the plate. These undesirable ef-' siderably more extensive than the anode when etching plates of the smaller sizes.

-The object of the invention is to provide an etching machine in which such irregularities do not occur or do not pass beyond acceptable limits. To this end, I make use of a form of cathode which is of open structure. By this term as used herein and in the claims, I intend to-inciude a structure such as a grid or a body having numerous perforations, which permits the free flow of liquid through it. The cathode also is curved so as to lie nearer to the anode at the centre than at outlying parts thereof, and with such a cathode I combine means for producing a flow of electrolyte through it towards or away from the anode. By this I secure circulation of the electrolyte, resulting in uniformity of electrolyte composition and absence of stationary bubbles or solid particles onthe surface which is being etched, as well as equality of distribution of the current over that surface.

The means for propelling the electrolyte through the cathode may be combined with the cathode or arranged behind it. The curved form of the cathode facilitates both of these arrangements.

In some ode from excessive etching. 6 i

In the following paragraphs, some practical embodiments of the several methods of attaining the object of the invention will be described with the aid of the accompanying drawings.

In these drawings, Figures 1, 3 and 4 show lon- 10 gitudinal sections through electrolytic etching machines arranged for etching flat plates. Figure 2 is a transverse section on the line 11-11 of Figure 1 and Figure 5 shows an end view of the cathode arrangement of Figure 4. 1 In the examples illustrated, the control of the paths for the current through the electrolyte is effected both by the shape and disposition of the cathode and by the use of barriers. In order to provide for the support of the plates by their edges, it'is convenient to use strips which extend across the bath at a short distance below the surface of the electrolyte and lie under the extreme edge of each of two opp i e sides of the plate. It is also convenient to niake these sup- 26 ports adjustable in position so as to deal with different, sizes of plates. In utilizing supports inthis way, it is also convenient to employ the support strips to form barriers for the control of the paths of the current between the anode 30 and the cathode. These barriers extend down- ,ward from the plate towards the cathode and exert a controlling influenceon the paths of the current on two sides of the plate. The effectiveness of these barriers depends, to a large extent, on the closeness. with which they approach the surface of the cathode.

In all the three examples illustrated, there are the common features of a tank I which is about two-thirds full of electrolyte, up to the line 2, and has supports for the plate 3 arranged so as to hold this just below the surface of the electrolyte. The tank also has,. running longitudinally through it, a rotary shaft 4 which carries means for producing agitation or circulation of the electrolyte. In the cases of Figures 1 and 3, the cathode is carried by and forms part of the agitating means. The tank is made of or internally lined with insulating material.

Where the plate 3 which is being etched is of zinc, it is preferable to make either of zinc or of insulating material all the parts which are immersed in the electrolyte. Other metal can be used but, in such cases, it should be coated with insulating material. Similarly, for etching other metals, it is desirable to have, in contact with the electrolyte, no metal which is different from that of the plate.

Along each of two sides of the tank near the level 2 of the electrolyte surface, runs a carrier bar 5 supported at each end in a bracket 6. These two bars serve as supports and guides for the two carrier strips 1 by which the plate 3 is held while being etched. These strips extend over practically the whole width of the tank and can be caused to slide along the bars 5 so as to obtain the right spacing between them to accommodate the size of plate which is to be etched. In the examples illustrated, comparatively small plates are being dealt with so that the cathode is considerably greater than the anode. These strips I extend downwards and have their horizontal lower edgeslocated a short distance from the upper part of the cathode. Theyform accordingly effective barriers to prevent excessive action on the edges of the plate 3 which rests on the support surfaces 8 of the strips.

Electrical connection is made with the plate 3 by the contact member 9, which consists of a disc in, of the same metal as the plate 3, and a casing of insulating material ll, serving. as a holder for the disc l0 and the end of the flexible connecting cable l2. The disc "I is recessed in the centre part of the lower face. Effective contact is secured by the weight of the contact member. No mechanical connection is made between the contact and the plate, so that the member 9 can readily be lifted away from the plate and replaced as required in the manipulation of the plate during the process of etching.

In the arrangement shown in Figures 1 and 2, the cathode is a perforated cylinder l3 carried on the shaft 4 by means of the end discs ll of insulating material. Electrical connection is made between the cylinder l3 and the shaft 4 by the flanged disc 15 which is placed adjacent to one of the discs l4. The remainder of the shaft within the tank is preferably enclosed in a covering of insulating material. The shaft is carried in bearings in housings l6 and projects at the right hand end where it is driven through a pulley l1, mounted on it, and receives current through a slip ring l8, also mounted on it, and

a brush l9 connected with cable 20. An examina-' tion of Figure 2 will show that, owing to its cylindrical shape, the cathode l3 approaches more nearly to the plate on the central plane of that figure than at .theoutlying parts. This makes for uniformity of action in the etching of the plate and prevents any excess of etching at the sides of the plate shown to the right and left of the centre in Figure 2. These are the edges of the plate which are not shielded by the barriers formed by the support strips 1. With this arrangement, a close approximation to uniformity of etching over the surface of the plate is obtained for a large range of plate sizes.

At each end of the cylinder I3 is mounted a centrifugal impeller 2| which communicates with the interior of the cylinder I3 through holes 22 in the disc l4. Each of these impellers is built up from a pair of discs mounted on the shaft 4 and a cylindrical ring carried between them and having a series of radial perforations 23 in it. The impellers are made of insulating material.

The action of these impellers, due to the rotation of the shaft, is to draw in through the perforations in the cathode cylinder l3 an electrolyte and carry it through the holes 22 into the impellers and then discharge it through the radial holes 23.

In order to avoid undue disturbance of the surface of the bath and to secure a thorough circulation of the electrolyte, the main portion of the upper surface of the bath is shut off from the end portions by walls 24 which extend downward from the top of the bath to a short distance below the level 2 of the electrolyte. The space between each of these walls 24 and the adjacent end ,of the bath receives the upward discharge from the periphery of an impeller 2|. The upper end of each of these narrow chambers is preferably enclosed but the enclosure is not necessar' ily complete, so that any gas liberated there can escape.

In the form shown in Figure 3, the cathode is also mounted on the shaft 4 so as to rotate and form part of the means for producing agitation or circulation. As in the case of Figure 1, the current is supplied to the cathode through the shaft 4 from slip ring l8, brush I9 and cable 20. The cathode consists of a number of rings 25 of metal which are interleaved with rings 26 of insulating material. These two sets of rings are held between end discs 21 by means of bolts 28 which also serve to carry current from the shaft 4 to the cathode rings. In this case, as in the case of Figure 1, the circular form of the cathode. at right angles to its longitudinal axis, has the effect of regulating the distribution of current between anode and cathode in planes at right angles to the axis of the shaft 4. In the case shown in Figure 3, there is, in addition, a similar regulation in vertical planes parallel with the axis of the shaft 4. This results from the fact that the discs 25 decrease in diameter from the centre of the cathode towards each end thereof.

The upstanding parts of the rings 26 between the cathode rings 25 serve as barriers and these also regulate to some extent the distribution of the current.

These rings 26 have radial perforations 29 which, in the arrangement shown in Figure 3, serve to produce the outflow of electrolyte radially from the cathode structure when the shaft 4 is rotated. The electrolyte can come into the interior of the rings 25 and 26 through passages 30 in the end plates 21. By this means, a circulation of the electrolyte can be obtained. Alternatively an arrangement similar to that in Figure 1 could be adopted by connecting impellers, such as 2|, to the outside faces of the plates 21. In that case, electrolyte would flow in through the perforations 29 and outward through the impellers 23, since the latter are of larger diameter than the rings 26.

In the example illustrated in Figure 4, the oathode is stationary, being formed as a grid structure consisting of bars 3|. As shown in Figure 5, these bars are of semi-circular form with outwardly projecting ends which are fixed in carrier bars 32 which are covered with insulating material. These bars 32 make electrical connection with insulated conductors 33 at each end of the bath. The grid is supported by brackets 34 carried on the end walls of the tank.

In this case, control of current distribution is obtained, not only by the semi-circular shape, but by the sub-division of the cathode into bars and the variation in the spacing of these bars which are closer together at the centre part of the tank than they are at the end. This is clearly shown in Figure 4. The agitation of the electrolyte is brought about by the cylinder 35 carried on the shaft l which has radial perforations 3i and end apertures 31. In this case, the electrolyte flows outward from the cylindrical surface of the cylinder 35. By combining this cylinder with two impellers 2|, arranged as shown in Figure 1, the flow of the electrolyte can be made inward at the surface of the cylinder 35 and-outward at the ends of the bath through the impellers.

The illustrative examples given in the drawings and the preceding description show how the conductance of the component parallel paths for the current between anode and cathodemay be varied from point to point. In the method in which the distance between anode and cathode varies from point to point, this variation may be obtained by making the surface of the cathode curved from the central region towards the sides. In Figures 1, 2 and 4, this curvature is shown as in a single plane. In Figure 3, there is curvature in two planes at right angles, one being due to the circular form of the cathode rings and the other to the variation in diameter of these rings. The cathodes have here been shown as of simple circular form. If this simple form does not completely suflice for obtaining the desired control of the distribution of the current, it may be supplemented by stationary metal parts placed on each side of the circular body. For instance, the bars 3! of Figure 5 may be extended sideways in an appropriate curvature.

The breaking up of the surface of the metal of the cathode, either by subdivision into separate parts, as in Figures 3 and 4, or by means of holes, as in Figure 1, has not only the advantages already referred to in describing those figures but also has the further advantage that in itself it tends to prevent local concentrations of current density on the anode.

It will be noted that the utilization of barriers at two sides of the plate does not prevent the free movement of the electrolyte resulting from the circulation or agitation produced by the rotation of the cathode or agitator.

What I claim as my invention is:

1. Electrolytic etching apparatus comprising a bath, means for supporting an anode to be etched in said bath and a cathode in said bath, said cathode being constituted by a number of spacially separated parts each of circular form and all arranged upon an axis parallel with the plane of the anode, said circular parts being spaced apart by distances which increase progressively from the middle part of the length of the cathode towards each end thereof.

2. Electrolytic etching apparatus comprising a bath, means for supporting an anode to be etched in the upper part of said bath, a cathode in said bath below said supporting means, said cathode being a hollow body of revolution disposed with its axis approximately horizontal and having openings in its curved wall and means for rotating said cathode about its axis, said body also constituting means for causing flow of the electrolyte through 4. Electrolytic etching apparatus comprising-a bath, means for supporting an anode to be-etched in said bath, a cathode in said bath, said cathode being constituted by a number of, parts all of circular shape and arranged coaxially and side by side and spaced apart, and rotary means acting-on the electrolyte on the concave side of said parts to move the electrolyte past the said parts and through the space between cathode and anode.

5. Electrolytic etching apparatus comprising a bath, means for supporting an anode to be etched in said bath, a cathode structure in said bath, said cathode structure being built up of circular rings of conducting material and concentric rings of non-conducting material disposed about the same axis, said non-conducting rings being perforated radially for permitting a flow of electrolyte through them, the radius of the first-mentioned rings decreasing progressively from the middle of the length of the cathode towards each end thereof and means for rotating the cathode about its axis.

6. Electrolytic etching apparatus comprising a bath, means for supporting an anode to be etched in said bath, a cathode in said bath, said cathode having anexternal conducting surface of circular curvature with'openings distributed over it, and rotary means surrounded by said surface and co-axial therewith for causing electrolyte to flow through the openings in the surface and substantially perpendicular to the anode.

. 7. Electrolytic etching apparatus comprising a bath, means for supporting an anode to be etched in said bath, a cathode in said bath in the form of a grid with parallel curved bars convex towards the anode, said bars being more closely spaced to each other adjacent that portion of the cathode opposite the center portion of the anode, rotary impelling means located adjacent to said grid on the concave side thereof for causing a positive flow of electrolyte through the grid substantially perpendicular to the anode.

8. Electrolytic etching apparatus comprising a bath, means for supporting an anode to be etched in said bath, a cathode in said bath, said cathode being of an open structure and being curved in general contour so as to be nearer the anode at the center thereof than at outlying parts thereof, the radius of curvature of the cathode being less than the radius of curvature of the anode and rotating propelling means placed on the side of the cathode opposite to that on which the anode is located for propelling the electrolyte through the cathode and toward the anode and substantially perpendicular to the anode.

9. Electrolytic etching apparatus comprising a bath, a cathode provided with distributed openings so that the electrolyte can flow through it and of curved form disposed in said bath so as to be convex upwardly, means substantially surrounded by and located within the concave side of the cathode and acting on the electrolyte therein to cause it to flow through said cathode and in substantially vertical paths thereabove, means for supporting an anode horizontally in said bath above the cathode, said supporting means comprising two bearers having ledges on which the edges of the anode may rest and be protected from excessive etching thereby.

10. Electrolytic apparatus comprising a bath,

means for horizontally supporting an anode tobe etched in the upper part of said bath, a

cathode in said bath below said supporting means, said cathode being a hollow body of revolution disposed with its axis approximately horizontal and having openings in its curved wall directed toward the anode and means located axially within the said wall for propelling electrolyte through the openings in the cathode. 11. Electrolytic etching apparatus comprising a bath, means for supporting an anode to be etched in said bath, a cathode structure in said bath in operative relation to said supporting means, the outer surface of said cathode structure comprising an arc, the are being such that it is nearest to the anode in the central region thereof, and gradually recedes therefrom in passing from the center towards the outlying parts thereof, openings in the outer surface of said cathode structure through which electrolyte can flow, and means substantially surrounded by the cathode and acting directly on the electrolyte therein to cause it to flow radially through the openings in the cathode and substantially perpendicularly to the anode.

12. Electrolytic etching apparatus comprising a bath, means for supporting an anode to be etched insaid bath, a cathode structure in said bath in operative relation to said supporting means, the outer surface of said cathode structure being of arcuate cross section in one plane and circular in a plane at right angles to the '--flrst-mentioned plane, the arrangement being 

